@import url('https://fonts.googleapis.com/css2?family=Montserrat:wght@500;700&display=swap');

body {
  margin: 0;
  font-family: 'Montserrat', sans-serif;
  background: linear-gradient(rgba(25, 50, 70, 0.85), rgba(10, 25, 40, 0.95)),
    url('https://images.pexels.com/photos/264630/pexels-photo-264630.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260') no-repeat center center fixed;
  background-size: cover;
  color: #e8f0f8;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 60px 20px;
}

.periodic-container {
  background-color: rgba(15, 35, 55, 0.9);
  max-width: 900px;
  padding: 50px 60px;
  border-radius: 20px;
  box-shadow: 0 0 50px rgba(50, 90, 130, 0.8);
  animation: fadeInZoom 1.5s ease forwards;
}

header {
  text-align: center;
  margin-bottom: 40px;
}

h1 {
  font-weight: 700;
  font-size: 3.2rem;
  letter-spacing: 1.5px;
  margin-bottom: 12px;
  color: #a3c1ff;
  text-shadow: 0 0 15px #5680f9;
}

.back-link {
  font-weight: 600;
  font-size: 1.15rem;
  color: #a3c1ff;
  text-decoration: none;
  border-bottom: 2px solid transparent;
  transition: border-color 0.3s ease;
  display: inline-block;
  margin-top: 15px;
}
.back-link:hover {
  border-bottom: 2px solid #a3c1ff;
}

h2 {
  color: #8bb7ff;
  border-bottom: 3px solid #5680f9;
  padding-bottom: 7px;
  margin-top: 35px;
  margin-bottom: 26px;
  font-weight: 700;
}

.intro p {
  font-size: 1.25rem;
  line-height: 1.75;
  max-width: 750px;
  margin: 0 auto;
}

.image-section img {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 28px auto;
  border-radius: 18px;
  box-shadow: 0 0 40px #5680f9cc;
}

.video-section iframe {
  display: block;
  margin: 32px auto;
  width: 100%;
  max-width: 560px;
  height: 315px;
  border-radius: 16px;
  box-shadow: 0 0 38px #5680f9aa;
}

/* Animations */
@keyframes fadeInZoom {
  0% {
    opacity: 0;
    transform: scale(0.95);
  }
  100% {
    opacity: 1;
    transform: scale(1);
  }
}